1. Field of the Invention
The invention relates to a method and apparatus for transmission of data and more particularly to a method and apparatus for transmitting speed information and other information detected by a sensing device.
2. Description of Related Art
Sensing devices that detect the speed of a moving object (rotary movement or linear movements) and transmit the information about the detected speed as well as additional information such as temperature, switching behavior, and direction of movement, to a control device, can transmit this information in various ways, which all tend to have certain problems associated therewith.
All of the information, i.e., the detected speed and the additional information detected, can be transmitted in parallel. This approach, however, requires additional lines and connections to the sensing device. The additional lines and terminals add to the cost and affect the reliability both during manufacture and operation. The additional lines and contact terminals on the sensing device and the internal wiring required inside a semiconductor chip in which such sensing devices are integrated, can result in EMI or EMV interference.
Another approach for transmitting the afore-mentioned information uses a very fast serial data protocol. In this approach, the speed information and the additional information are transmitted sequentially. In comparison to parallel transmission, no additional lines or contact terminals on the sensing device are required. The data protocol, however, must be transmitted relatively fast so that all the information is transmitted within an acceptable time.
Yet another approach for overcoming the disadvantages uses a so-called multilevel analog transmission. This transmission of the information, however, requires an extremely accurate calibration of the sensing device and/or an extremely accurate measurement. Problems with this transmission technology can arise, particularly if the sensing device is subjected to severe temperature fluctuations.
It is therefore desirable to provide a method of the type described above which is much simpler and much less susceptible to errors than the conventionally employed transmission methods. The method may also allow a relatively low-frequency serial data transmission over two-wire lines. It would also be desirable to provide a sensing device for carrying out such a transmission method.